Multiple pregnancies now account for 1.5% of all pregnancies.
The commonest form of multiple pregnancies are twins, though triplets, quadruplets and order higher order multiple pregnancies are occasionally seen as well. Such higher order multiple pregnancies have even higher risks than twins.
In twins, there are 3 main types of placentation:
Dichorionic diamniotic (DCDA) - "Di" stands for 2, "chorion" refers to the placenta, and "amnion" refers to the amniotic sacs. Hence DCDA twins refer to twin pregnancies with separate placentas and separate amniotic sacs. The majority of DCDA twins are fraternal (i.e. non-identical twins) though a small percentage of the liked-sex DCDA twins are identical.
Monochorionic diamniotic (MCDA) - "Mono" stands for 1. Hence MCDA twins refer to twin pregnancies with a single shared placenta and separate amniotic sacs. Almost all MCDA twins (with very few exceptions) are identical.
Monochorionic monoamniotic (MCMA) - MCMA twins refer to twin pregnancies with a single shared placenta and single amniotic sac. These are identical twins as well. Such twin pregnancies are associated with the highest risk as there is a high probability of cord entanglement between the twins caused movement and entanglement of the cords between the 2.
The diagnosis of the chorionicity is easily achieved by ultrasound scan between 7-14 weeks as the presence of a twin peak sign denotes DCDA twins while the absence of a twin peak sign denotes MC twins.
Due to the shared vascular anastomoses in a MC placenta, MC twins have additional specific vascular risks of:
10-15% risk of twin twin transfusion syndrome (TTTS)
10-15% risk of selective intrauterine growth restriction (IUGR)
2-5% risk of twin anaemia polycythaemia sequence (TAPS)
Risks of death / brain damage to co-twin if one twin dies
In addition, both DCDA and MC twin pregnancies are also at increased risks (compared to singleton pregnancies) of:
exaggerated symptoms and signs of pregnancy e.g. nausea and vomiting
preterm labour (PTL)
intrauterine growth restriction (IUGR)
gestational diabetes mellitus
Twin pregnancies, especially monochrionic twins, are high risk pregnancies that have to be monitored closely with ultrasound. It is recommended that monochorionic twins and dichorionic twins are monitored every 2 weeks from 16 weeks and 2-3 weeks from 20 weeks respectively.
Progesterone pessaries may be useful to reduce spontaneous preterm delivery amongst twins with short cervix.
Mode of delivery for twins
If twins are delivered below 32-34 weeks, Caesarean section may generally be safer.
If twins are delivered from 32-34 weeks, the options for mode of delivery depend on the position of the first twin and whether there are any complications that may make it risky for vaginal delivery. If the first twin is not head down and / or there are complications that make it risky for vaginal delivery, Caesarean section may be the safer option. If the first twin is head down and there are no complications that make it risky for vaginal delivery, either vaginal delivery or Caesarean section may be chosen.
A successful vaginal delivery is generally less risky for the mother (i.e. better and faster recovery) but may be associated with a small chance of difficulty in delivering the second twin. It is advisable to opt for an epidural if one is attempting vaginal delivery in twins as the epidural allows manipulation of the second fetus vaginally to either head down position or buttocks down position after the first twin is delivered, and also allow a shorter interval to Caesarean section if necessary. It is also associated with lower risk for the next pregnancy. Of course, an attempt at vaginal delivery may also result in an emergency Caesarean section for both twins or, less commonly, for the second twin after a successful vaginal delivery of the first twin.
A Caesarean section, on the other hand, imposes slightly more risks to the mother (e.g. higher risks of bleeding, infection, possible injury to other organs), less surprises for delivery of the second baby, and slightly more risks in the next pregnancy (e.g. possible adhesions, increased risks of Caesarean section, uterine rupture if trying for a vaginal birth in the next pregnancy, and placenta accreta and unexplained stillbirth in the next pregnancy).
You need to discuss the options thoroughly with your doctor.